JJHerb@aol.com on sat 28 dec 96
The most common kind if manometer is a U-tube manometer - a tube with two
vertical, parallel arms with a scale, often in inches, between the arms. As
an initial condition, the tube has an amount of liquid, often water, in it
and the level is the same in each leg. One leg of the U is connected to the
source of pressure, the other is open. When the pressure is applied to the
manometer tube, the water in the open side of the tube rises until the water
column equals the applied pressure. Measuring the difference between the two
water surfaces gives the pressure reading in Inches Of Water. If the
pressure is too great, the water is blown out of the tube and you no longer
have a manometer, just a U-tube. In olden times, a manometer might contain
mercury.
The pressure of 1 psi is about 27 inches of water column. A pressure of 1
psi is about 2 inches of mercury column. The diameter of the tube does not
matter. The length of the connecting tube to the pressure source does not
matter. Floating crud in the water may matter. A petcock on each of your
burner inlet pipes and a long plastic tube will allow you to hang up (or
permanently nail) your manometer in a single location and read each burner
supply setting individually by connecting the long tube to each petcock in
succession. If you fix the U-tube in place and make a provision for moving
the scale, you can position the zero point of the scale at the same level as
the lower of the water levels and then directly read the number of inches to
the other water level. This eliminates the necessity of having to subtract
numbers, some of which could contain fractions.
In high school physics lab we constructed these things with Tygon tubing and
a Meter stick. Manometers are also used to make pitot tube measurements in
air handling systems, so a heating/air conditioning supply company is a
possible source, if you don t want to make your own.
Joseph Herbert
JJHerb@aol.com
Karl P. Platt on fri 29 aug 97
Dwyer's Magnahelic gauges are a fine alternative to a U-tube or inclined
manometer -- I haven't seen a manometer used in 15 years -- and then it
was used by an old-timer. They're on $60.00 or so at Grainger's and
their use can pay back the 60 pilha very quickly in gas savings and
consistent results
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